Electrical capacitors



May 31, 1960 J. H. COTTON ETA!- 2,939,050

ELECTRICAL CAPACITORS Filed Jan. 15, 1957 a a A INVENTORS T 1 5 E JAMES H. corro/v FEL/X 8. 14 5/55 1,;9. Wad),

ATTOKA/f) United States Patent ELECTRICAL CAPACITORS James Henry Cotton, London, England, and Felix S.

' Weiss, West Newton, Mass., assignors to Cornell- Dubilier Electric Corporation, South Plainfield, NJ., a corporation of Delaware Filed Jan. 15, 1957, Ser. No. 634,236 Claims priority, application Great Britain Sept. 4, 1956 5 Claims. (Cl. 317-260) This invention relates to electrical capacitors of the rolled type, in which metal and dielectric layers are spirally wound into a roll, the metal layers of opposite polarity being connected respectively to terminals at opposite ends of the roll. The metal layers may be constituted by metal foils strips or alternatively by metallized coatings on the dielectric strips. In the former case, the metal foil strips are often arranged to project beyond the edges of the dielectric strips, the projecting edges of the metal strip or strips of one polarity being at one end of the roll and those of the other polarity at the other end of the roll, and the terminals are usually pressed into engagement with such projecting edges and secured thereto by soldering. In the latter case a generally similar arrangement is often used, each metallized coating being spaced away from one edge of the dielectric strip by a demetallized area but being taken right up to the other edge of the strip so as to make contact with solder applied to the end of the roll to secure the terminal thereto. In other instances, the metal foil strips or the metallized coatings are spaced away from both edges of the dielectric strip, narrow metal tabs being inserted in appropriate positions in the roll in contact with the foils or coatings so as to project beyond the ends of the roll for soldering to the terminals. Each terminal usually includes a piece of wire, which is intended to project centrally from the end of the roll, but with all these alternative known arrangements it is diflicult to ensure satisfactory centering of such terminal wire. Moreover, considerable care has to be taken in handling. the capacitor element, when manufactured in accordance with the known arrangements, owing to the comparative weakness of the joint holding the terminal in place. Thus, with the very thin metal foil used for the electrodes (usually of the order of only five or six microns), a lateral stress on the terminal can very easily tear the projecting ends of the foils, so that the terminal breaks away from the capacitor. To minimize this risk, it is usual to employ relatively thin and flexible terminal wires, which is often a matter of considerable inconvenience.

j The present invention has for its object to provide a relatively strong terminal joint for a rolled capacitor, wherein accurate centering of the terminal on the end of the roll is readily and easily achieved.

The rolled capacitor according to the invention comprises metal and dielectric layers wound spirally into a roll, a metal foil tab inserted in theroll in contact with one of the metal layers and projecting from one end of the roll, such tab being wide enough to extend at least for the major part of a turn in the roll, a terminal having a central conductor projecting from a circular base which substantially fits the projecting end of the metal tab, and means for securing the base of the terminal to the projecting end of the metal tab, whereby the central conductor of the terminal is held properly centered in position relatively to the capacitor roll. Such terminal fitting is preferably employed at both ends of the roll, two similar metal foil tabs being inserted in the roll in contact respectively with metal layers of opposite polarity and projecting respectively from opposite ends of the roll, each such tab receiving end being secured to a terminal in the manner described.

Preferably, the base of the terminal or of each terminal engages within the cylinder or part cylinder formed by the projecting end of the associated metal tab and may be secured thereto by soldering. The edge of the metal tab is preferably bent inwardly over the base of the associated terminal being soldered thereto. The terminal or each terminal may conveniently be of the pigtaiP type formed by bending a single piece of wire so that one end portion thereof forms a circular rim constituting the base of the terminal while the other end portion forms the central conductor.

Alternatively, the base of the terminal or of each terminal may be in the form of a disc, to the center of which the central conductor is secured, the edge of the disc being upturned and then again turned back on itself to form a circular groove within which the projecting end of the associated metal tab is secured.

The invention may be carried into practice in various ways, but some convenient practical arrangements of rolled capacitor in accordance therewith are illustrated by way of example in the accompanying drawings, in which Fig. l is a perspective view of one construction of capacitor roll before the terminal is secured thereto;

Fig. la shows an alternative construction of capacitor roll;

Figs. 2 and 3 show one construtcion of terminal respectively in perspective view and in end view;

Figs. 4 and 5 are diagrammatic views showing two stages in the process of securing the terminal of Figs. 2 and 3 to the capacitor roll;

Fig. 6 is a diagrammatic view illustrating. another arrangement; and

Fig. 6a illustrates a further alternative terminal construction.

In the arrangement of Fig. 1, the capacitor roll 1 is formed in the well known manner by spirally winding two strips of metal foil with intervening dielectric strips, which are of greater width than the metal foil strips so that there is a margin of dielectric beyond both edges of the metal strips. Alternatively, the roll may be formed by spirally winding two metallized dielectric strips, with or without intervening unmetallized dielectric strips, the metallized coating on each metallized dielectric strip being narrower than the strip itself so as to leave an unmetallized margin at both edges of the strip. The dotted lines 10 and 11 indicate the levels in the roll of the side edges of the metal layers, leaving the margins 12 and 13 of the dielectric strips free from metal layers. The two wound metal layers, whether constituted by foil strips or by metallized coatings, constitute the two electrodes of the capacitor, and connections are taken from them to terminals at opposite ends of the roll 1.

For this purpose, two metal foil tabs 2 and 6 are inserted in predetermined positions in the lengths of the strips, so as to be wound into the roll, these two tabs being respectively in contact with the two electrodes. One of these tabs 2 is positioned so that one of its ends projects beyond one side edge of the adjacent dielectric strip, its other end however being spaced well away from the other edge of the dielectric strip, so that in the finished roll the end of the tab will project from one end of the roll 1. The other tab 6 is similarly arranged so that one of its ends will project from the opposite end of the roll 1. Each tab preferably has a width such that it will extend for nearly one complete turn in the roll, so that its projecting end will be in the form of an incomplete cylinder,

but it may extend for a complete turn or more, if desired. The large width of the tab ensures that it will be firmly gripped in the roll. The two tabs 2 and 6 lie against consecutive or nearly consecutive turns of the two electrode layers, so that their projecting cylindrical ends will have substantially the same effective diameter. These tabs will usually be made of thicker foil than the electrodes themselves, for example of the order of one or two thousandths of an inch, and may be made for example of tinned copper.

Although in the above arrangement the metal layers, whether foil or coating, have their edges spaced away from the edges of the dielectric strips, the invention is equally applicable to other arrangements, for example wherein the metal layers are in the form of metallized coatings each extending right up to one edge of the dielectric strip and spaced away from the other edge, or wherein the metal layers are in the form of metal foils, each projecting beyond one edge of the dielectric strip and spaced away from the other edge.

The latter arrangement is illustrated diagrammatically in Fig. la, wherein the same reference numerals as in Fig. l are utilized where applicable. The metal foil of one polarity projects beyond the edges of the dielectric strips at one end of the roll, as indicated at 14 (where the upper part of the roll is shown broken away to enable the foil edge to be seen), while its other edge indicated at 14a is spaced away from the other edges of the dielectric strips leaving a margin 13. The metal foil of the other polarity projects beyond the edges of the dielectric strips at the other end of the roll, as indicated at 15, while its other edge indicated at 15a is spaced away from the edges of the dielectric strips leaving a margin 12. The metal tab 2, which is in contact with the metal foil 14, 14a, projects beyond the projecting edge 14 of this foil, its other end being indicated at 17. The metal tab 6, in contact with the foil 15, 15a, likewise projects beyond the edge 15 of this foil, at the other end of the roll, its other end being indicated at 16.

In the arrangement of Figs. 2-5, the terminal used at each end of the roll ll, which may be of any of the kinds above described, is of the well known pigtail type formed by bending a single length of wire, so that one end portion forms a generally circular rim 4, constituting the base of the terminal, the wire then passing to the centre of such circle, where the remaining portion of the wire extends at right angles to the plane of the rim 4 to constitute a straight central tail 3. The diameter of the circular rim 4 is such that it will substantially fit within the cylindrical projecting end of either metal tab 2 or 6, as indicated at one end of the roll 1 in Fig. 4. It will be clear that this arrangement ensures accurate centering of the central tail 3 of the terminal, with respect to the capacitor roll 1.

For securing the terminal to the metal tab 2., the edge of the cylindrical projection of the tab is bent inwardly over the rim 4 of the terminal, as indicated at 5 in Fig. 5, thus holding the terminal firmly in place, and the joint is completed by soldering the parts together. The terminal is preferably heavily tinned, thus rendering unnecessary the use of flux for the soldering to the tinned metal tab. One advantage of using an incomplete turn for the metal tab is that the small gap in its cylindrical projection facilitates soldering and enables a suitably shaped soldering iron to approach more readily to the parts to be joined together.

Where there are projecting metal foil edges, as in the arrangement of Fig. la, or where the electrodes are in the form of metallized coatings extending right up to one edge of the dielectric strips, the solder may extend over the whole end of the roll, so as to secure the edge of the metal layer also to the tab and to the terminal.

The turning over of the tab edge on to the rim 4 of the terminal provides much greater mechanical strength in the joint than has hitherto been obtainable by known 4 methods of soldering capacitor terminals, and this in turn makes it possible to use thicker gauge wire for the terminal itself without risk of tearing away in subsequent use. Such stiffer terminal wire can be more easily kept straight in use and is of considerable advantage in mounting the capacitor wherever it may be required.

The arrangement is of considerable advantage when used in association with automatic winding equipment, wherein it is easy to arrange for correct positioning of the meta tabs, so that their projecting cylindrical ends will have the correct diameter for receiving the terminals.

It should be mentioned that the rim 4 of the terminal may be flattened into the form of an annular disc, if desired, before insertion into the cylindrical end of the metal tab. In a further variant, shown in Fig. 6a, the terminal is in the form of a fiat disc 7, with a central conductor 9 firmly secured to its center point, the diameter of the disc being such that it will substantially fit within the projecting cylinder of the metal tab, so that the edge of such cylinder can be bent inwardly over the edge of the disc before soldering.

It will be appreciated that it is not essential to the arrangement to bend the edges of the tabs over the circular rims of the terminals, and in such case the centering would be equally effective, but the soldered joint would have less mechanical strength.

Fig. 6 shows an alternative arrangement, in which the terminal consists of a straight wire 9 secured at right angles to the centre of a disc 7, whose edge '8 is bent upwardly and then downwardly again to form a circular groove. The size of this groove is such that it will receive the cylindrical end of the metal tab, and the joint may then be completed by soldering or staking or clinching or welding or other convenient means.

With either arrangement, the capacitor roll fitted with its terminals at both ends may be enclosed by molding or otherwise in any suitable casing, in the manner well known in itself.

It will be clear that two or three standard sizes of terminal will suit a wide range of different sizes of capacitor the metal tabs being carefully positioned in the roll to suit the size of the base of the terminal.

It will be appreciated that the foregoing arrangements have been described by way of example and may be modified in various ways within the scope of the invention. For example, the terminal fitting according to the invention may be used at one end only of the capacitor roll, the electrode of the opposite polarity being connected to a metal casing in the manner known in itself.

In accordance with the provisions of the patent statutes we have herein described the principles of this invention, together with the elements which we now consider to constitute a workable embodiment thereof, but we desire to have it understood that the structure disclosed is only illustrative and the invention can be carried out by other means. Also, while it is designed to use the various features and elements in the combinations and relations described, some of these may be altered and modified without interfering with the more general results outlined.

Having thus described our invention, we claim:

1. A terminal construction for convolutely wound roll capacitors having at least one relatively thin electrode element included therein comprising a discrete tab element of conducting material of a thickness substantially greater than that of said electrode element wound into said roll in electrical contact with the electrode element and sized so that one edge thereof longitudinally extends beyond the end of said roll and circumferentially extends over at least the major portion of one convolution thereof, a terminal member having a substantially circular base portion disposed against the end of said roll and sized to be disposed closely within the arcuate extremity of said tab and engaged thereby and an extending lead portion disposed in substantial alignment with the ax1s of said roll.

2. A terminal construction for convolutely wound roll capacitors having at least one relatively thin electrode element included therein comprising a discrete tab element of conducting material of a thickness substantially greater than that of said electrode element wound into said roll in electrical contact with said electrode element and having the edge portion thereof longitudinally extending beyond the edge of said roll and circumferentially extending over at least the major portion of one convolution thereof, a terminal member having a substantially circular base portion disposed against the end of said roll and sized to be closely contained within the convolution of said extending port-ion of said tab element and an extending lead portion disposed in substantial alignment with the axis of said roll and means securing said extending edge portion of said tab member to said encircled base portion of said terminal member.

3. A terminal construction for convolutely wound roll capacitors having at least one relatively thin electrode element included therein comprising a terminal member having a substantially circularly rimmed base portion disposed against the end of said roll and an extending lead portion disposed in substantial alignment with the axis of said roll, a discrete tab element of conducting material of a thickness substantially greater than that of said electrode element wound into said roll in electrical contact with said electrode element having an extending end sized to circumferentially extend over at least a major portion of one convolution thereof and disposed in closely encircling engagement with at least the rim of said base portion of said terminal member and means securing said extending portions of said tab member to said base portion of said terminal element.

*4. A terminal construction for convolutely wound roll capacitors having at least one relatively thin electrode element included therein comprising a terminal member having a substantially circularly rimmed base portion disposed against the end of said roll and an extending lead portion disposed in substantial alignment with the center of said roll, a discrete tab element of conducting material of a thickness substantially greater than that of said electrode element wound into said roll in electrical contact with said electrode element having an extending edge portion of circular configuration disposed in closely encircling engagement with the base portion of said terminal member and means securing said extending edge portion of said tab element to said base portion of said terminal member.

5. A terminal construction for convolutely wound roll capacitors having at least one relatively thin electrode element included therein comprising a discrete tab element of conducting material of a thickness substantially greater than that of said electrode element wound into said roll in electrical contact with the electrode element therein sized so that one edge thereof extends beyond the end of said roll at least for one convolution thereof, a terminal member having a substantially circular base portion disposed against the end of said roll and sized to be closely disposed within the convolution of the extending edge of said tab element and overlayingly engaged thereby, a terminal lead member extending from said base member and disposed in substantial alignment with the axis of said roll and means securing the extending edge of said tab element to the base portion of said terminal member.

References Cited in the file of this patent UNITED STATES PATENTS 2,470,045 Nagy May 10, 1949 FOREIGN PATENTS 239,839 Switzerland Mar. 1, 1946 850,925 Germany Sept. 29, 1952. 

